The present invention relates generally to wireless communication networks comprising a plurality of radio base stations for communicating with mobile terminals, and, more particularly, to a method of balancing backhaul delays for a series of radio base stations connected in a daisy chain to a base station controller.
In a mobile communication network, the service area is divided into a plurality of cells, each of which is served by a radio base station. Each base station comprises radio resources for communicating with local terminals within the cells served by that base station. A number of radio base stations can be connected to a single base station controller, typically via leased T1 or E1 lines. A common network topology used to connect multiple radio base stations to a single base station controller is a star topology. In the star topology, each radio base station connects to the base station controller via a dedicated line. The star topology is an efficient topology for routing data packets between a base station controller and multiple radio base stations. A disadvantage of the star topology is that it requires a dedicated line between the base station controller and each radio base station, which increases the cost of operating the network.
In order to save leased line costs, some network operators use a daisy chain topology to connect multiple radio base stations to a single base station controller. In a daisy chain topology, the radio base stations are connected in series with the base station controller. The first radio base station in the series connects directly to the base station controller. Each subsequent radio base station connects to the previous radio base station. Thus, more than one radio base station can share a single leased line to the base station controller. Instead of connecting directly to the base station controller which may be far away, a radio base station may instead connect to a neighboring radio base station which is much closer. Using a daisy chain topology can result in a significant reduction of leased line costs to the network operator. However, the daisy chain topology is not without its disadvantages.
One disadvantage of the daisy chain topology is that the transmission delays between the base station controller and the radio base stations may be significantly increased, particularly for the radio base stations toward the far end of the daisy chain. A number of factors may contribute to transmission delays, including packet queuing delays and processing delays in each radio base station in the daisy chain. Thus, each hop along the daily chain adds additional delay to packets being delivered. The amount of the transmission delay is directly related to the number of hops that the data packet traverses to reach the intended radio base station. Radio base stations at the far end of the daisy chain will experience longer delays than will radio base stations closer to the base station controller. For some applications, particularly ones that can tolerate large latency periods, these delays will not be critical. Other applications, such as voice or streaming applications, are more sensitive to transmission delays. In these applications, longer delays mean a lower quality of service.